1. Field of the Invention
The present invention relates to methods and means for the remote installation and/or removal of nozzle dams onto and from nozzle holddown rings within the channel heads of the type of steam generators typically used in conjunction with the operation of nuclear power plants. The instant invention relates to methodology, together with specially designed tooling, for remotely introducing through an open channel head manway tubesheet tackle means and the securing of same therein, followed by inserting through said open manway a folded nozzle dam, and thereafter causing the opening of said dam together with the proper translocation, orientation, and securing of same relative to and onto said nozzle holddown ring. This practice is followed by inserting, orientating, and securing the center portion of said nozzle dam means and thereafter torquing all bolting means to predetermined limits. Removal from said channel head of all said attendant tubesheet tackle means along with other asunder apparatus is, of course, also contemplated before the channel head is rendered ready for various testing.
At periodic intervals during the operation of boiling or high pressure water, nuclear-fired, power or propulsion systems there are necessitated the occurrence of system outages such as when refueling of the nuclear reactor is to be performed or repairs are to be effected within any of the numerous water circulating loops. During such outages, it is usual for the level of the primary coolant water within the system to be lowered to a level below that of the inlet and outlet pipes extending to and from the reactor, which pipes are typically horizontally disposed therebetween. In the vernacular of this art, such procedures are known as drain-down. More specifically, in the type of reactor system which serves several vertical inverted U-tube type steam generators, the draining down is usually effected through both the chemical volume control system and the residual heat removal system, from which the draining water is led into holdup tanks. For reasons obvious to those skilled in this art, such draining down is conducted only after the system has been cooled and depressurized by releasing steam from the steam generators, shutting down the main circulating coolant water pumps, depressurizing the pressurizer, and starting the residual heat removal pumps to actuate the residual heat removal system.
Typically, during such drain-down procedure, a gas which is inert to the system, such as nitrogen, is introduced into the system through the top of the system pressurizer tank to displace the water which is draining from the system. As the water is drained from the pressurizer, whose discharge flows into one of the "hot legs," or reactor outlet conduits, which leads to the bottom of one of the steam generators, the nitrogen introduced through the pressurizer will eventually begin to disperse throughout the system from the bottom of said pressurizer. The nitrogen first enters the reactor above the water level therein via the reactor outlet conduit to which the pressurizer is connected, and then passes via all of the reactor inlet and outlet conduits, which are oftentimes horizontally disposed at the same elevation, to the respective steam generators and main circulating pumps in the respective steam generation loops.
As will undoubtedly become more readily apparent from a reading of the teachings of the instant invention, infra, it is inherent in the design of such systems that a total drain-down thereof would effect a lowering of the water level therein to such an elevation that the fuel rods placed in the spent fuel pit would not be covered in water, a most undesirable and untenable situation. This will be more fully appreciated when it is realized that the difference in elevations of the spent fuel pit and a channel head of a typical steam generator in one nuclear plant system for which the instant invention was designed and tested is about 50 feet. Accordingly, it is desirable, and perhaps more importantly necessary, to partially reverse such drain-down procedure at the appropriate stage to ensure that work may proceed concurrently on both the primary and the secondary sides of the system even after adjusting the system water level upwards.
From an inspection of a system typical of the type herein referenced, it will be appreciated that the juxtaposition of the nozzle holddown ring and the outlet conduit of the channel head provides a situs suitable for closing or blocking off water flow back into the channel head upon subsequent raising of the system water level. Since no apparatus or mechanism such as, for example, a valve or plug, is present at this situs, one, or an equivalent thereof, has to be introduced thereinto. Accordingly, the nozzle dam means referred to, supra, generally comprising a gasketed plate adapted for operative association with the nozzle holddown ring, is the usual means which is introduced and secured at such situs to seal off the opening of the nozzle holddown ring and effect closure of the steam generator outlet conduit. Once this nozzle dam and its companion, i.e., one each for the steam generator outlet conduit and the steam generator inlet conduit, is secured, the raising of the water level in the system will not act to flood the respective channel head into which such nozzle dams are secured. Of course, if more than one steam generator is operatively associated with the reactor, the respective nozzle dams in each of the channel heads would likewise be secured. Because the only viable means of ingress to the channel head is the manway therein provided, and further, since the inside diameter of said manway is typically one-half that of the outer diameter of said nozzle dam, said nozzle dam is provided with hinging means to allow for the folding thereof. This design criteria results in a discontinuity occurring right down the middle portion of such sealing means, which design may prove to be less than desirable for effecting a positive seal. Accordingly, a substantial portion of each half of said dam is usually removed or left out, during the fabrication thereof so that a center portion of the nozzle dam may be fitted and tightly secured in a manner which effectively overcomes the disadvantages otherwise associated with, and the location of, such discontinuity. Also, of course, such a design consideration helps reduce the weight of the dam.
As to the feature of the instant invention which relates to said tubesheet tackle means and the securing of same, it has been noted, supra, that the tubesheet provides little in the way of opportunity for attachment. Accordingly, it has been common practice in such instances to employ the use of devices for attaching to the inside surfaces of the tubes.
It has long been known to employ various means to expand a device within a tube as a way of gripping the tube from within its internal diameter. While there are many examples of this art, one of the more commonly known methods is the plug of the type used in Thermos.TM. bottles. In this prior-art design, a rubber plug that is slightly smaller than the hole is squeezed between two end restrictions to cause it to expand radially into contact with the inside of the tube diameter and thus become wedged into the hole.
One application of a tubesheet internal tube gripper is a grapple attached to the inside of the tubes of tubesheets of the type typically found in a nuclear steam generator. Periodically it is necessary to perform maintenance or inspections from within the heads of these very large heat exchangers. Typically such a steam generator has some 3,000 or more tubes originating in a tubesheet above a channel head, which head is generally a hemisphere usually ranging between about seven to eight feet in diameter. When maintenance or inspection is performed, it is necessary to hang equipment such as closed circuit television cameras, pulleys, safety lights, certain other test fixtures, and other items from the tubesheet. Since the tubesheet surface is usually a layer of Inconel.TM., magnetic clamps cannot be used. Furthermore, each of the tubes is welded into the flat tubesheet, so that the tube holes present the only likely surface to which an attachment can be made.
The simple expanding plug, such as that used in a Thermos.TM. bottle, supra, is effective for light loads. Since it relies only on friction, it cannot withstand heavy loads if the coefficient of friction is reduced due to wetness or other contaminant on the inside tube surface.
A substantial improvement on the expanding plug means, supra, has been fairly recently developed and comprises a shaft member including an upper tapered portion, surrounded by a generally cylindrical sleeve member, having at least two holes opposite the tapered portion of the shaft. The sleeve outer diameter is slightly less than the inner diameter of the tube to which the attachment is to be effected. Spring means are connected between the shaft member and the sleeve member for biasing the tapered shaft downwardly relative to the sleeve. A metal ball is located in each hole such that downward motion of the shaft relative to the sleeve urges the balls outwardly to protrude from the sleeve surface against the tube wall. For convenience and ease of reference, this improved device is herewith referred to as a rapid installation tube gripper.
Only the tubesheet tackle means and not the securing of same with the use of a specially designed tackle insertion tool means according to the instant invention, is based, at least in part upon the design of the rapid installation tube gripper, supra; however, as will be appreciated from the more detailed description, infra, the instant design and utilization substantially further improves upon the art of inside tube grapplers in general, and more specifically of such rapid installation tube gripper.
As to the feature of the instant invention which relates to said suitable nozzle dam strapping means, which is to be operatively associated with said nozzle dam, it will be understood that in the preferred embodiment of the instant invention the strapping means are first secured to the nozzle dam means. Alternatively it may be inserted, with the aid of a tackle insertion tool through said open manway, from a remote location outside the channel head and subsequently properly secured to the still folded nozzle dam, which dam has previously been inserted into the channel head. The principal purpose of said strapping means is to effect the subsequent opening of said nozzle dam and the translocation and proper positioning of same onto the nozzle holddown ring. With the aid of the nozzle dam rotation tool and the alignment pin tool or video camera, the proper orientation of same relative to said nozzle holddown ring is also effected. As described, supra, both the nozzle dam rotation tool and the alignment pin tool are manipulated, through the open manway, by operator(s) who are located outside said channel head and the resulting properly aligned nozzle dam is temporarily secured to the nozzle holddown ring with the aid of bolt starting tool means. Since some of the activities of said operators must be coordinated, one with the other, said operators oftentimes wear headphones to facilitate communication with each other and, in some instances, support personnel in standby mode including Radiological Control Group (RAD-CON) monitoring of radiation exposures, doses, etc. The inserting, orientating, and securing of the center portion of said nozzle dam means is also accomplished with the aid of at least a portion of the strapping means, i.e., the two 25-inch intermediate length straps of the six normally utilized, as well as with the use of an appropriate hook pole and bolt starting tool. The reverse procedure, i.e., the removal of the nozzle dam may also be effected with the aid of these apparatuses.
As to the feature of the instant invention which relates to said other tooling, for example, the various nozzle dam rotation tools, bolt starting tools, tube marking poles, mirror poles, tackle insertion tool, alignment pin tool, hook poles, the specific designs, as well as the functions and operations thereof, will be described in some greater detail, infra.
2. Description of the Prior Art
As has been noted, supra, several prior-art investigators have discovered, taught, and disclosed methods and/or means for attaching to the inside surface of tubes so as to provide for means to secure and hang various asunder equipment from the tubesheet. An example of such prior art is found in the teachings and disclosure of U.S. Pat. No. 4,643,472, Schukei, et al., Feb. 17, 1987. Schukei, et al., describe a rapid installation tube gripper which generally comprises a shaft member including an upper tapered portion surrounded by a generally cylindrical sleeve member having at least two holes opposite the tapered portion of the shaft. The sleeve outer diameter is slightly less than the inner diameter of the tube targeted for attachment. Resilient means are connected between the shaft member and the sleeve member for biasing the tapered shaft downwardly relative to the sleeve. A relatively small metal ball such as, for example, a ball bearing, is located in each hole such that downward motion of the shaft relative to the sleeve urges the balls outwardly to protrude from the sleeve surface against the tube wall.
According to the teaching of Schukei, et al., their device is installed by pushing on the stem means at the lower end of the shaft member to insert their device into the tube. A stop means, such as a flange, is formed at the lower end of the sleeve to limit the sleeve insertion into the tube. In this way, the tapered portion may be pushed longitudinally upward relative to the holes, whereby the balls are retracted into the sleeve and their device may be installed into or removed from the tube.
A device only somewhat similar to that of Schukei, et al., is employed in the practice of the instant invention in providing attachment means onto the tubesheet. Said device, herein referred to as tubesheet tackle means or simply tubesheet tackle or just tackle, comprises a shear plate to which at least one shaft member, having such upper tapered portion, is rigidly attached together with at least one, and preferably two tapered insertion pins. Said at least one shaft member and said pins are spaced one from the other on said shear plate to align with three predetermined tube apertures, preferably arranged in triangular relationship, one from the other. This arrangement effects substantially improved stability of the instant new apparatus well beyond that provided by prior-art devices. Also, instead of the use of flange means, located at the lower end of the sleeve for effecting movement thereof relative to said tapered shaft and resulting retraction of the balls, the instant device employs a retracting ring attached on one side of the spring biased movable sleeve for engagement with a tackle insertion tool at or near the lower end thereof, which lower end is spaced horizontally above said shear plate when said device is orientated in the proper insertion and attachment mode.
This new and improved arrangement allows for the utilization of a tackle insertion tool in combination with said tackle to effectively and remotely provide attachment means on said tubesheet, whereas the device of Schukei, et al., supra, is designed and adapted for attaching to the tubesheet primarily by hand, thereby requiring ingress of an operator into said channel head. As discussed in greater detail in Example I, infra, an attempt was made to provide a companion insertion tool to operate in unison with said normally hand-held Schukei, et al., device, but proved to be quite inadequate.
Applicants are presently unaware of any prior art, either in the patent literature or in the offerings and listings in currently circulated vendors' catalogs which teach, disclose, or in any way lead towards the teachings of the instant invention other than that just discussed, supra.